Method for fabricating isolation layer in semiconductor device

1. A method for fabricating a field oxide in a semiconductor device, the method comprising the steps of: forming a pad oxide film and a pad nitride film sequentially on a semiconductor substrate defining a cell region and a peripheral region; forming a trench on the semiconductor substrate by etching the pad oxide film, the pad nitride film and the substrate; forming an oxide film of side walls on a surface of the trench; depositing an amorphous silicon film on a resultant substrate inclusive of the trench; etching the amorphous silicon film so that the trench is partly filled with amorphous silicon; depositing an insulation film on a resultant substrate so that the partly filled trench is filled completely; carrying out a CMP process of the insulation film to expose the pad nitride film; and removing the pad nitride film.

2. The method as claimed in claim 1 , wherein the amorphous silicon film is deposited to a thickness thinner than the depth of the trench.

3. The method as claimed in claim 1 , wherein the amorphous silicon film is deposited thicker than half of a width of the trench in the cell region, and is deposited thinner in the peripheral region than the thickness of the amorphous silicon film deposited in the cell region.

4. The method as claimed in claim 3 , wherein the amorphous silicon film is deposited to a thickness more than 60 nm, when a width of the trench is 120 nm.

5. The method as claimed in claim 1 , wherein the etching of the amorphous silicon film is carried out to remove it to a depth just below the surface of the substrate.

6. The method as claimed in claim 1 , wherein the amorphous silicon film is formed in an atmosphere of a mixed gas made of SiH 4 and N 2 at a deposition temperature ranging from 500 to 600° C.

7. The method as claimed in claim 1 , wherein the insulation film is deposited to a thickness ranging from 300 to 5000 â„«.